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ISSN: 0973-4945; CODEN ECJHAO

E-Journal of Chemistry

http://www.e-journals.net Vol. 4, No. 3, pp. 354-362, July 2007

Determination of Tellurium(IV) in Various

Environmental Samples with Spectrophotometry

P. REDDY PRASAD, J. DILIP KUMAR, B. KRISHNA PRIYA,

P. SUBRAHMANYAM, S. RAMANAIAH# and P. CHIRANJEEVI*

*Environmental Monitoring Laboratories,

Department of Chemistry,#Department of Geology,

S. V. University, Tirupati-517502, India.

Received 10 December 2006; Accepted 10 February 2007

Abstract: A rapid, simple and sensitive spectrophotometer method for thedetermination of traces and ultra traces of tellurium(IV) were studied. These

method were based on either the oxidation of leuco methylene green (LMG) to

its blue form of methylene green by tellurium in acidic medium, the formed dye

shows an absorption maximum at 650 nm in acetate buffer medium (pH 3.0 to

5.0). Beers law were obeyed in the concentration range 0.4 2.5 g mL-1,

having molar absorptivity and Sandals sensitivity of 4.9104 L mol-1 cm-2 ,

and 0.0026 g cm-2

, respectively. The optimum reaction conditions and other

analytical parameters were investigated to enhance the sensitivity of the present

method. The tolerance limit of various ions with this method has been studied.

The proposed method was applied for the analysis of tellurium in spiked, river,

lake, spring, waste water samples, plant materials and soil samples. The results

obtained by the proposed method were superior to the reported method. The

performances of proposed methods were evaluated in terms of students t-testand variance ratio f-test which indicates the significance of proposed methods

over reported methods.

Keywords: Te(IV), Leuco methylene green (LMG), Spectrophotometry, Environmental samples.

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355 P. CHIRANJEEVI et al.

Introduction

The Tellurium and its compounds were widely used in thin films, rechargeable batteries andcharge transfer systems etc. Tellurium exposure may result in garlic-like breath. The

Tellurium aerosol irritates the eyes and the respiratory tract. The substance may cause

effects on the liver, central nervous system, abdominal pain, constipation and vomiting.

Tellurium is widely used as semiconductors and occurs in small quantities in inorganic

materials and biological samples. It is also a potential environmental pollutant. Tellurium

enters into natural water through seepage from soils and industrial waste. Many analytical

techniques such as Voltammetry1, Flame atomic absorption spectrometry

2, Atomic

absorption spectrometry3,4

, Inductively coupled plasma-mass spectroscopy5,7

, Inductively

coupled plasma-atomic emission spectroscopy8,9

, X-ray fluorescence10,11

and

Electrophoresis12 have been employed for tellurium analysis in various environmental

matrices. This increased the interest in developing rapid, sensitive and simple methods forthe determination of traces of tellurium.

Several reagents have been employed for the spectrophotometric determination of

tellurium in various matrices like bismuthiol13

, N-phenylbenzohydroxamic acid14

, tetra

methylthiourea15

, xylenol orange16

, salicylfluorone17

and ion association complex such as

TeIV

Cl-

- cationic violet18

, TeIV

Br-

butyl rhodormin-B19

, TeIV

Br-

- acridine20

,

TeIV

- I-

rhodormin B-poly vinyl alcohol21

and TeIV

- I-

rhodormin B-poly vinyl alcohol -

OP22

systems have been used for the determination of tellurium (IV) by ion pair complex

methods. The above reported methods suffer from several drawbacks such as low

sensitivity, selectivity and acquire extraction18,20. The sensitivity of TeIV- I- rhodormin B-

poly vinyl alcohol21

, TeIV

- I-

rhodormin B- poly vinyl alcohol -OP22

and TeIV

- tungstate-

basic dyes- poly vinyl alcohol

23

were moderate however, the stability ion-pair complexeswere very poor. So, it is desirable to develop simple, sensitive, reliable, rapid method for the

determination of tellurium in various samples.

A survey of literature reveals that few spectrophotometric methods associated with

ion-pair complexes were proposed for the determination tellurium in environmental samples.

Here, for first time the, authors reported simple, rapid and sensitive method for the

determination of traces of tellurium in various samples with oxidation process. The reaction

was oxidative coupling and the product is highly stable than the methods reported in

literature. The experimental variables affecting color formation and the possible tolerance of

foreign ions were thoroughly studied. The optimum conditions established were

incorporated in the investigation of tellurium(IV) in various environmental samples.

Experimental

Instrumentation

A Hitachi U 2001 spectrophotometer with 1.0 cm matched quartz cell was used for all

absorption measurements. A pH meter Elico Li-129 Model glass calomel combined

electrode was employed for measuring pH values.

Reagents and solutions

All chemicals used were of analytical reagent grade and deionised - double distilled water

was used to prepare all solutions through out experiments. Working solutions of the Tellurium(IV)

oxide was prepared by dilution of the corresponding standard solutions 1000 mg L-1

(Merck, Mumbai, India) with doubly - deionised distilled water. 1% leuco methylene

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Determination of Tellurium(IV) in Various Environmental Samples 356

green (from B.D.H., Poole, UK) was prepared by dissolving 1.0 g of leuco methylene

green in water and diluted up to the mark in a 100 mL standard flask with deionised - double

distilled water and the solution was refrigerated.General Procedure

Stock solution containing 1 to 100 g (0.03 3.5 mL-1) of tellurium (the volume of the test solution

was restricted to 1 mL) were transferred into 25 mL calibrated flask and 5 mL of Leuco methylene

greenreagent (Scheme 1) mixture were added followed by 3 mL of Acetate buffer. The mixture

was allowed to stand for 5 min for the completion of the reaction. The contents were diluted up to

the mark with doubly-deionised distilled water and the absorbance was measured at 650 nm against

the corresponding reagent blank and the calibration graph was constructed.

Determination of tellurium in natural water samples

The proposed method were employed for different natural water samples (river, lake, spring)

(200 mL each) collected around Tirupati area. The samples were used directly to measure thetellurium(IV) contents by the proposed methods after filtered with cellulose membrane of pore

size 0.45 m as mentioned in literature24

and determined by above general procedure.

Determination of tellurium in waste water samples

The distillation procedure for the determination of tellurium in waste water as follows: To an aliquot

(100 mL) of known sample taken in a distillation flask, 1 g of KBr and 10 mL of concentrated H 2SO4

treated with 0.5 mL of saturated bromine water were added and the solution was then distilled under

vacuum till copious white fumes of SO3 vapours were evolved, and this process converts all other

forms of tellurium in to tellurium(IV). The distillate was collected in 10 mL of 5 % hydroxyl

ammonium chloride solution, then made up to a fixed volume and analyzed by the general procedure.

Determination of tellurium in vegetable samples

5 g of finely chopped fresh tomato and brinjal samples each were placed in a 500 mL beaker

and 10 mL of a 1:1 (v/v) mixture of concentrated sulfuric acid and nitric acid were added.

This solution was heated, until the mixture was clear. Then the solution was filtered and

concentrated to 5 mL, cooled and diluted up to 50 mL with doubly-deionised distilled water.

The general procedure was employed to 1 mL of this solution for analysis of tellurium.

Determination of tellurium in soil sample

A known weight of tellurium was mixed with 20 g of soil sample, fused with 1:1 sodium

carbonate and potassium nitrate mixture in a nickel crucible and extracted with water. The

filtrate of the extract was treated with 20 mL of 10 mol L-1

hydrochloric acid and then

heated to expel chlorine and oxides of nitrogen. The solution was further diluted with water

to give a suitable concentration of tellurium. An aliquot of the stock solution was passed

through the cation exchange resin (Amberlite XAD- MB-3A) to remove the iron present in

soil. The tellurium contents were determined as described in the general procedure.

Results and Discussion

Absorption spectra

The absorption spectra of the leuco methylene green with tellurium show maximum

absorbance at 650 nm. Reagent blank showed negligible absorbance at this wavelength.

Beers law was obeyed over the concentration range 0.4-2.5 g mL-1

of tellurium per 25 mL of

the final solution at 650 nm. The apparent molar absorptivity and Sandells sensitivity were

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Figure 1.Absorption spectra of Te(IV) with leuco methylene green

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

480 520 560 600 640 680 720 760 800

Wavelength(nm)

Absorbance

Te(IV) with leuco Methylenegreen

Reagent blank


found to be 4.9 x 104

dm3

mol-1

cm-2

and 0.0026 g cm-2

respectively. Repeatability of the method

was checked by the replicate analysis of the working standard solution containing 3 g per 25 mL

of tellurium over a period of seven days and absorption spectra was shown in Figure 1.

Effect of pH concentration

The effect of pH on the peak height of tellurium(IV) at different concentrations wasinvestigated with a fixed reagent concentration (1.0% leuco methylene green) in the pH

range of 3.0 5.0 and the peak height was measured for each concentration level of

tellurium(IV). At all concentration levels of Te(IV), maximum peak heights were found

between pH 3.0 5.0. Therefore, a pH 4.0 was selected for further studies.

Optimum conditions for color product formation

In order to establish the optimum conditions necessary for a rapid and quantitative formation of the

colored product with maximum stability and sensitivity, the investigators measured the absorbance

of a series of solutions by varying one and fixing the other parameters at 650nm. It was found that a

1.0 % solution of leuco methylene green in the range of 2.0 - 4.0 g mL-1, was necessary to achieve

the maximum color intensity of the oxidative coupling product. The color intensity decreased below

the lower limit and above the upper limit, and a blue colored product was unstable. Therefore,

3.5 mL of Leuco methylene green was recommended for all measurements.

Effect of temperature on colored product

The reaction between leuco methylene green in to tellurium(IV) was found to be instantaneous.

The effect of the temperature on the product was studied at different temperatures; it was found

that the colored product was stable for more than 7 days in the temperature range of 25 40oC.

So, the temperature of 350C was selected as optimum for maximum color development.

Ringbom plot for blue colored derivative

Ringboms plot is the established standard adopted to know the optimum range of concentration

for a system that obeys Beers law. The plot is drawn between log Cof tellurium(IV) and (1-T)

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Figure.2 Ring bom's plot for Te(IV) with leuco methylene green

0

0.5

1

1.5

2

2.5

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6

log c

(1

-T)


(where Tis the transmittance). The plot has a sigmoid shape with a linear segment at intermediate

absorbance values (0.1 to 1.8) and concentration values (0.2 to 0.2 g mL-1

). The slope of

Ringboms plot from Figure 2 is 1.85. Hence, the ratio between the relative error in concentrationand photometric error is 0.2 , for a concentration of 0.2, for 90 % photometric error.

Optical parameters

Beers law range, molar absorptivity, Sandells sensitivity, and other parameters of the

oxidative coupling mixture were given in (Table 1). The precision and accuracy of the

method was studied by analyzing the coupling solution containing known amounts of the

cited reagents within Beers law limit. The low values of the standard deviation (%) and the

percentages of error indicated the high accuracy of the present investigation.

Table 1. Optical characteristics and precision data

Parameters/CharacteristicsLeuco methylene

green (LMG)

Color Blue

max , nm 650

Beers law range, g mL-1

0.2-2.5Molar absorptivity, L mol

-1cm

-24.9 x 10

4

Sandells sensitivity, g cm-2

0.0026

Regression equation (Y)*

Slope (a) 1.85

Intercept (b) 0.0146

Correlation coefficient (r) 0.99971

Standard deviation, %+

0.68

Range of error (95 % confidence level) 1.2

% error 0.137*Y=ax+b, where x is the concentration of tellurium in g mL

-1,

+n=4

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Reaction mechanism

Under the reaction condition, tellurium(lV) is reduced by taking 2e- in Leuco methylene

green molecule and changed into methylene green. The reaction mechanism of oxidativecoupling is carried out in Scheme 1.

Interference of foreign ions

The effect of various species on the determination of Te(IV) was investigated. The tolerance

limit was taken as the amount that caused 2% absorbance error in determination of

3 g mL-1

Leuco methylene green of tellurium. The results were shown in Table 2.

Table 2. Effect of foreign species on the determination of 3 g mL-1

tellurium with

Leuco methylene green (LMG).

Species Tolerance limit, g mL-1

EDTA 10500

Na+, Mg

2+,Cl

-, NO3

-, F

-, CHCOO

-, CO3

2-, K

+2080

Ba2+

, SO42-

, CN-, SCN

-, Tartarate 1090

PO43-

, Al3+

, Cd2+

,aNO2

-810

bCu

2+, Ni

2+b, Co

2+b, Ca

2+86

b

Zn2+

, Pb2+b

, SO32-

, NO3-, Cr

3+, As

5+55

Fe2+a

, S2-

40

Se+4b

1000a Can be masked up to 850 g mL-1 by the addition of 3 mL of 2 % sulphamic acid.b Can be masked up to 90 g mL-1 by the addition of 3 mL of 5% EDTA.

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Applications of the method for determination of tellurium(IV) and statistical

comparison with reported method

The proposed methods for the determination of tellurium(IV) has been employed for real

samples of water, plant materials and soil of tellurium were presented in Table 3. The

obtained results were compared with the reported method 23 in terms of studentst-test and

f- test. The analytical data summarized in Table 3 suggest that the percentage recovery of

tellurium(IV) from water, plant materials and soil ranges from 98.00 to 99.45 %, which is

more reliable and sensitive than other methods. Analysis of tellurium(IV) in various

matrices reveals the sensitivity of proposed method.

It is evident from the above data that the proposed method was simple, rapid and

more sensitive than the reported methods in the literature as shown in Table 4.

Table 3. Determination of traces of tellurium(IV) in various samples.

Sample

Proposed method Reported method23

Tellurium

added,g

Tellurium

found,g

Recoverya

%t-test f-test

Tellurium

added,g

Tellurium

found,g

Recoverya

%

Spiked water I

0.20 0.196 98.00.46 5.05* 0.96* 0.20 0.19 95.00.46

Spiked water IIb

0.40 0.395 98.750.43 3.03* 0.23* 0.40 0.39 97.500.43

Waste waterb

-

0.60

0.23

0.82

-

98.790.39 5.89* 0.53*

-

0.60

0.091

0.67

-

96.660.39

River waterb -

0.80

0.36

1.14

-

98.270.36

- - -

Lake waterb

-

1.0

0.18

1.17

-

99.150.68

- - -

Spring waterb -

1.20

0.08

1.26

-

98.330.23

- - -

Plant materialsb

Tomato

-

1.40

0.10

1.49

-

99.330.23

- - -

Brinjal -

1.60

N.D.

1.59

-

99.370.68

- - -

Soil sampleb

-

1.80

0.04

1.83

-

99.450.45 2.69* 0.95*

-

2.0

0.014

1.984

-

98.500.36

an = 4,

bLeuco methylene blue, N.D. = Not Detectable,

*Where P = >0.0004. Samples are collected from around Tirupati area.

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Table 4. Comparison of proposed methods with reported methods for spectrophotometer

determination of tellurium(IV) in various samples.

Reagentsmax

nm

Molar

abosrptivity

L mol-1cm-1

Remarks

References

TMT 382 2.14104

Less sensitive [2]

NPBHA 345 3.5 104

High reagent consumption and needs

extraction

[1]

Xylenol

orange

569 2.82 104

Commercial reagent, low detection limit,

Bi+3

, In+3

and Ti+3

ions interfere seriously

[3]

Salicyl

fluorine

534 1.47105

Interference effect is more, less selective [4]

Cationic

violet

590 4.5104

More time and reagent consuming method,

need solvent for extraction of color species

[5]

RB 560 2.8 104

Less selective, high interference effect [9]

Ethyl violet 560 1.55 104

Low sensitive and having less stability [10]

ismuthiaol II 330 3.64 104

Hg+2

, Se+4

, Fe3+

and Sb3+

interferes

seriously

[13]

-phenylbenzoydroxamic

cid

635 2.37 105

Needs elaborate process and benzene wasused for extraction

[14]

NB/RB/BRB 580/

565/

565

3.3310 /

1.76106/

1.88106

Less stability, moderate interference effect [23]

Leuco

methylene

green

650 4.2104

Highly stable and selective, rapid, free

from interference effect.

This

work

Conclusions

The proposed spectrophotometric methods for the determination of tellurium in varioussamples are facile, rapid and sensitive than the reported methods in literature

23. These

methods have added advantages over reported method23

owing to its:

i) Coupling reagents employed in the present methods were fairly soluble inwater, very cheap and readily available in market.

ii) The oxidative coupled color derivatives formed in proposed methods werequite stable when compare to reported method in the literature

23, which

enhances the sensitivity of the present methods.

iii) Statistical analysis of the results indicates that these methods have goodprecision and accuracy.

Thus the method can be adopted as an alternative to the already existing methods

(ion-pair complexes).

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Acknowledgements

The authors are grateful to Head, Department of Biotechnology, S.V. University, Tirupati,

for providing instrumental facility.

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